January 10, 2013

Astronomers Discover Hundreds Of New HII Regions In The Milky Way

A new survey of the Milky Way has uncovered hundreds of previously-unknown regions of massive star formation, including some of the most distant located to date in the galaxy, researchers revealed on Wednesday.

Using the National Science Foundation's (NSF) Green Bank Telescope (GBT) in West Virginia and the Arecibo Observatory Telescope in Puerto Rico, as well as data from the NASA-operated Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE) satellite, astronomers were able to find regions where massive young stars were forming, both individually and in clusters.

Those zones, which scientists refer to as HII regions, “serve as markers of the Galaxy's structure, including its spiral arms and central bar,” the researchers explained in a statement on Wednesday.

Continued study of these objects, whose discovery was presented during the American Astronomical Society (AAS) meeting in Long Beach, California this week, could give researchers “crucial clues about the structure and history of the Milky Way,” they added.

Boston University´s Thomas Bania, one of the astronomers behind the study, said that their work is “vastly improving the census of our Galaxy, and that's a key to understanding both its current nature and its past history, including the history of possible mergers with other galaxies.”

According to the researchers, they started out by using only the GBT to seek out HII regions and compile a survey of the Milky Way. They did so by hunting for faint emissions of hydrogen atoms at radio wavelengths that were not obscured by the dust contained in the galaxy´s disk, known as radio recombination lines (RRLs). By detecting those RRLs, the survey team was able to more than double the number of known HII regions in our galaxy.

“They continued that work using the Arecibo Telescope, finding additional objects, including the largest HII region yet found, nearly 300 light-years across,” they said, crediting the sensitivity of the two telescopes for much of their success. “Data from previous surveys with radio and infrared telescopes, including Spitzer and WISE, helped to guide the new search. Later work analyzed similar emissions of helium and carbon atoms.”

One of the astronomers, West Virginia University´s Loren Anderson, said that data obtained from WISE shows approximately 2,000 new HII-region candidates that they are currently studying using the GBT to confirm. In addition, the researchers are studying chemical variations in different regions of the Milky Way, seeking out variations in the abundance of heavier elements in an attempt to chronicle the history of star formation.

"We've already been surprised to learn that the thin, tenuous gas between the stars is not as well-mixed as we thought," said Dana Balser, of the National Radio Astronomy Observatory (NRAO). "Finding areas that are chemically different from their surroundings can point to where gas clouds or smaller galaxies may have fallen into the Milky Way.”

"Just as geologists traverse the landscape, mapping different rock types to reconstruct the Earth's history, we're working to improve the map of our Galaxy to advance our understanding of its structure and its history. The radio telescopes are our tools for making these new and better maps,” Bania added.